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CAS TOPICS => Gunsmithing => Topic started by: RUSS123 on January 12, 2020, 04:35:47 pm

Title: Excessive CB Gap, need professional opinion.
Post by: RUSS123 on January 12, 2020, 04:35:47 pm
Hi all, new to this forum and this is my first post.

I'll get right to the point: New Uberti 1872 Open Top, 7.5" .38 Special, purchased from Cimarron.

My initial inspection, I noticed visually that the BC gap looked a bit wide. I had not taken the gun apart yet. The BC gap measured .012" with cylinder pulled to the rear. End shake was hardly perceptible at half cocked.  The wedge had been pounded hard. I had to use a brass punch to remove the wedge.

Pulled the barrel, then, checked the Arbor for frame/barrel "overlap" as per Pettyfogger's instructions. There was some overlap but not much. Then I slid the barrel back onto the Arbor to remeasure the BC Gap at the point where the bottom of the barrel and frame come together, then lightly tapped in the Wedge. I could not press the wedge in by hand to where it exited even a little on the opposite side of the barrel. I just gave it a light tap with a safety hammer to hold it in place to do a second BC Gap measurement. What I did should be equal to an Arbor correctly seated with the barrel, as if corrected with a spacer.

The BC Gap measured .018" and of course end shake increased by .006" which I expected.

The thing is, whoever assembled this gun at the factory severly pounded in the wedge to force the barrel in toward the cylinder to provide a "reasonable?" looking BC Gap with little to no end shake.

What I realize is this: If the Arbor interface were to be corrected with the barrel, the BC Gap is going to be enormous. I can't figure any other way to correct the BC Gap spacing error without literally milling about .012" off the bottom of the barrel to frame fit at the two pegs. The front Cylinder bushing would also need to be cut back as well.

Is this correctable or a wash?

I have not contacted Cimarron yet about warranty repair. Not sure that I even want to. What if they say: Well, that's in spec and that's what you get with these guns. Not sure I would even trust their repair. I would be more willing to spend the money for a professional to correct it and tune it all up, if it's possible. I don't want the headspace to be sacrificed to tighten a huge BC Gap.

Please tell me what you think. Am I overlooking something? I need to convince Cimarron that I have a valid repair request.

I'll appreciate all responses.
Title: Re: Excessive CB Gap, need professional opinion.
Post by: 45 Dragoon on January 12, 2020, 07:23:45 pm
RUSS123,
   The Barrel assy is supposed to contact the frame where the locating pins are (no gap. I'm sure you know that, didn't want you to think I'm being a smart asp). That could be considered the fulcrum or the pivot in the open top design. The fact that the arbor bottoms out in the arbor hole is what determines the barrel/cyl clearance. I say clearance so most folks in the blk powder world will know what I'm talking about. To modern revolver folks it is understood as endshake. It's not truly a "gap" unless there is a bushing  that actually keeps the cyl face and forcing cone from contacting each other. So, if your revolver has a bushing, it will have a bbl/cyl gap. If it just has a gas ring (prevents cyl binding from fouling) it probably should be an endshake situation. Obviously, if neither a bushing or ring are present, it's definitely an endshake situation.  The nice thing about endshake setups is they can be as close as .0015" - .003" because the cylinder and barrel do meet .  .  .  each time the action is cycled!! They're self cleaning!!!

  So, since you have an Uberti, the arbor is in deed short. My own way of correcting the problem is by installing a single spacer of the correct thickness down the arbor hole. I use JB Weld to keep it in place. I leave the spacer a few thousandths thick so I can "fine tune" to the targeted  spec.  by removing material from the end of the arbor (making it even shorter!!!).  Once the desired spec is reached, the wedge can be driven in and your spec will always be there! Make sure you do all the adjusting with the wedge in with full tension.
  You may also want to drill the end of the arbor through to the wedge slot and thread it. You can then install a set screw (face ground flat ) to act as a wedge bearing .  .  .  an adjustable wedge bearing. You'll never need to replace your wedge not to mention, you can customize the wedge "depth" that it goes in to accommodate easier re-holstering. It may not be a problem with your revolver but it can be a problem on some cap guns.

Mike
Title: Re: Excessive CB Gap, need professional opinion.
Post by: Coffinmaker on January 12, 2020, 07:51:48 pm
DISCLAIMER:  I only made a living as a CAS gunsmith for about 20 years before I retired.  I was also a specialist for the 1871/72 Open Top

It's simple actually.  Barrel to cylinder gap is optimal at .005/.006 and .018 is unacceptable.  The 1871/72 Open Top has a Gas Ring integral to the Cylinder.  You should be able to seat the wedge far enough to engage the retaining screw with a light tap with the butt of a plastic screwdriver.  End Shake at that point (you have a gas ring - end shake is an issue) should be .002 and your Head Space between cartridge head and recoil shield is optimum at .004/.005.  These amounts are achieved with the wedge seated properly and the retaining screw snug.  If the Wedge also puckered the sides of the barrel lug, it needs replaced.

Your gun doesn't meet any of that criteria.  SEND IT BACK.  In fact, SEND IT BACK for REPLACEMENT.
Tell Cimarron the same thing you have explained here.  DO NOT attempt to fix it.  DO NOT allow anyone else to fix it.  They (Cimarron) owe you WARRANTY.  Also, don't shoot it.  You or anyone else taking tools to it WILL VOID the warranty.

Title: Re: Excessive CB Gap, need professional opinion.
Post by: RUSS123 on January 12, 2020, 09:50:46 pm
Thank you both, 45 Dragoon (Mike) and Coffinmaker,

It's a "Gas Ring" I was referring to. Sorry, lack of nomenclature on my part.

I had downloaded all the articles written by Pettiefogger and read them through several times to be able to talk about it with the understand. I'm no stranger to revolvers. I own 5, 3 of which are Ruger SAs and have measured BC Gaps, head space, end shake, lockups, etc. so it's easy to visually know when a gap appears excessive. I at least know what's operationally essential.

This gun, from my mechanical perspective has no solution outside of cutting material from the face of the barrel mounting where the locating pins go in, in order to bring the forcing cone close enough to the cylinder which would also require to cutting back on the Gas Ring of the cylinder. That would be ridiculous of course but if it were the only open top in the world and your only option, it could be done and all could be good. I don't know if what I'm concluding was every done.

For my own interest, I would love to know what went wrong.

I have not shot it yet.  You both have convinced me that I have a viable warrant replacement request. I will be in contact with Cimarron tomorrow.

By the way Mike.... did you not see my request for service on you web sight. I'm still interested in what you can do for a full tuning service once I get back a gun that's tune-able, so to speak. I also want to have a Ruger style hand spring installed.

It's a shame really! The action on this gun was already quite smooth.

Thanks again...
Title: Re: Excessive CB Gap, need professional opinion.
Post by: 45 Dragoon on January 12, 2020, 10:21:48 pm
Hey Russ,

   I did see your email late last night. Sorry I didn't call you. It's been the most unexpected week ever! Last Sunday my wife and her brother took their dad to visit an assisted living facility they had located 2days before. Long story short, we moved him in yesterday!!  So, it was all hands on deck getting his furniture, clothes, new bed stuff, bathroom stuff, T.V. (of course!!) pictures hung from Thurs-Sat. morn. .  Needless to say he was very familiar with his new place!!
  I'm just glad my wife doesn't have to worry about her dad on a daily basis .  .  .  very stressful .  .  .  for 3 yrs!!
  We are both looking forward to a more normal "life" so.

I'll pm ya. Thanks again and thanks to C.M. for your "headspace" info. forgot the dummy cartridge thing!!

Mike
Title: Re: Excessive CB Gap, need professional opinion.
Post by: RUSS123 on January 13, 2020, 12:32:21 am
Hey Russ,

   I did see your email late last night. Sorry I didn't call you. It's been the most unexpected week ever! Last Sunday my wife and her brother took their dad to visit an assisted living facility they had located 2days before. Long story short, we moved him in yesterday!!  So, it was all hands on deck getting his furniture, clothes, new bed stuff, bathroom stuff, T.V. (of course!!) pictures hung from Thurs-Sat. morn. .  Needless to say he was very familiar with his new place!!
  I'm just glad my wife doesn't have to worry about her dad on a daily basis .  .  .  very stressful .  .  .  for 3 yrs!!
  We are both looking forward to a more normal "life" so.

I'll pm ya. Thanks again and thanks to C.M. for your "headspace" info. forgot the dummy cartridge thing!!

Mike

Mike, I know how that is with aging parents. I helped take care of my wife's mother who came to live with us for 9 years. The last 2 years of her life was very stressful on both of us before she died at the age of 92. Fortunately, we had Hospice help in the last month of her life. She died peacefully one Sunday morning. Hospice was a huge help.

Anyway, I did a more precise and careful measurement. I neglected to realize the affect the bolt can have on measurements and it's why you put your gun at half cocked to have the bolt out of the way. On a Ruger, you just open the gate to bring down the bolt.

So..with wedge pounded in as it was in the box: BC Gap measured:

.012" cylinder forward
.0135" cylinder to the rear
.0015" end shake
.004" head space

Wedge reasonably set with just a light tap of the hammer: BTW, the wedge wouldn't even go in far enough to lock it in with the wedge screw.

.015" cylinder forward
.024" cylinder to the rear "(hard to believe but true)"
.009" end shake

Before asking anyone's opinion about these findings, I was considering to just send it to you for a tuning job anyway, assuming you would fix the spacing as well. Doesn't sound like it's possible with such errors now. Is it?

I'm not in a rush. This, like many other adventures in firearm troubleshooting, design and education, has been a real pleasure.

At this point: When I talk to Cimarron tomorrow and if they agree, they will issue me an RA number to ship for warranty repair.
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